This invention relates generally to the joining of interfitting elements, and has more particular reference to the joining and sealing of telescoped tubular elements such as pipes and pipe sockets that are composed of thermoplastic material and joined together in an electrical welding or fusion process.
A well known predecessor of this invention is disclosed in U.S. Pat. No. 3,506,519, in which a welding sleeve of thermoplastic resin, having a coil of electrical resistance wire embedded in the resin, is clamped in a pipe joint between an outer, socket element of the joint and an inner element in the form of a pipe that is fitted into the socket element. The ends of the wire forming the heating coil extend out of the joint for connection to a power source, for example, as in U.S. Pat. No. 3,465,126. During the fusion process, the joint is squeezed by a clamp that is applied to the joint around the telescoped elements and tightened to squeeze the elements together during fusion.
As explained in U.S. Pat. No. 3,506,519, this electrical welding process fuses the elements of the joint while they are held in intimate contact, and restrains the articles against thermal expansion, as well as compensating for certain mismatches in size. Most importantly, this process joins the articles together in a homogeneous structure that provides a secure, leakproof joint.